The field of this invention relates to antennas and more particularly to a feedhorn that is to be used to receive and transmit the downlink signal from a satellite to a receiver such as a television set.
Use of satellites in broadcasting of television programs is exceedingly common. The use of satellites constitute a much less expensive method of transmitting television programs as well as substantially increasing the fidelity of the transmission. Additionally, satellites make available a great many channels for sending out of television programs.
The use of a satellite dish antenna permits a single homeowner to get the television programs directly eliminating the need to pay a service fee to a local cable television company. Also, the individual homeowner has a big advantage in that he/she has a substantially increased selection over that what the local station chooses to rebroadcast.
A television's program trip by satellite starts at the uplink, where the program is put on the carrier. The carrier is one of a band of frequencies cluster around six gigaHertz, or six billion (6,000,000,000) cycles per second. This microwave frequency is chosen because, among other things, it can be focused into a narrow beam by dish antennas of practical size and because it penetrates quite well through moisture and dust in the atmosphere. Uplink antennas are usually thirty feet across which are a good balance between cost and efficiency.
The dish-shaped antenna, which are exceedingly familiar in conjunction with satellite signal transmission and satellite signal receiving, are really parabolic reflecting mirrors acting like the parabolic mirrors utilized in conjunction with search lights. The uplink antenna sends the signal out in a narrow beam because the signal must be sent to a particular satellite. The beam from the uplink must go in the right direction within about one-tenth of a degree.
Each satellite carries a plurality, of transponders with each transponder providing a complete separate electronic path from incoming signal to outgoing signal. Each transponder is tuned to one of the standard bands near six gigaHertz. Tuning the uplink signal to the right band, activates the desired transponder.
Each transponder has two modes, that is, a horizontally polarized signal and a vertically polarized signal. Thus, the program carrying ability of each transponder is doubled with each polarized signal capable of carrying a single television program. The more material the single satellite can carry, the less expensive the system.
Each transponder of the satellite converts a signal to one of many standard frequencies clustered around four gigaHertz for the downlink signal. This is referred to as the C-Band. Now satellites are being constructed to include a second band which is at a frequency much greater than the four gigaHertz of the C-Band. This second band being referred to as the Ku-Band. This Ku-Band is in the range of twelve gigaHertz.
The satellite transmits the downlink signal on a broad beam that covers a large area. Each receiver assembly on earth starts with a dish-shaped parabolic antenna that captures a segment of the energy being beamed down and focuses such into the receiving equipment. The larger this antenna, the more efficient the receiving of the energy. In the past, most home antennas have been in the range of nine to twelve feet for a good balance between cost and performance.
The size of these dish-shaped antennas (nine to twelve feet in diameter) is being judged by an increasing number of residential communities as being unattractive in appearance. Installation of such antennas is prohibited in such communities. Therefore, usage of these antennas are becoming limited to the rural communities. However, if the size of this antenna could be substantially diminished, then possibly the usage of these antennas would not be restricted within residential communities.